The aim of this proposal is to analyze the molecular and cellular events leading to progenitor cell (hepatoblast) and hepatocyte formation, in embryonic liver explant cultures. Although first described over explant cultures have not been clearly defined. We have successful established this in vitro system established this in vitro system and proceeded to utilize it as an assay in preliminary antisense studies to two genes elf and prajal, both fully cloned and isolated by us (31, 32). These loss of function studies have resulted in extremely interesting morphological phenotypes: loss of liver architecture formation in prajal experiments, and the loss of hepatocyte differentiation in the elf studies. However, the subsequent cell types obtained cell types obtained still need to be characterized. The first part of this project studying the expression of liver and biliary tree markers in the in vitro liver explant cultures. For instance, in order to identify a hepatoblast phenotype, markers such as alpha-fetoprotein albumin and cytokeratin 14 (CK14), and c-kit will be utilized. Markers indicative of bile duct lineage such as CK14, CK 19 and gamma-glutamyl transpeptidase will also be used. Explant cultures will be harvested on a temporal basis for the delineation of such hepatoblast to hepatocyte and bile duct formation. Studies will then be extended to determine the differentiation potential of the in vitro explant cultures under different substrate conditions, such as carrying concentrations of matrigel, gelatin, tissue culture plastic, DMSO and sodium butyrate. The second part of this proposal will involve the analysis of functional antisense experiments to elf and prajal utilizing the explant cultures. These studies will be carried out with both in- house and outside collaborations involving Drs. J. Bernstein and W. Goldberg (VAMC), and Dr. A. Rashid (JHU). The study of such in vitro explant cultures not only promises to a better understanding of liver formation, but also may in the future be utilized for tissue engineered composites as form of liver restoration therapy.